Users expect items cleaned in an automatic dishwasher to be not only clean but also clear (i.e. lack of filming and spotting). Cleaning presents a great challenge for the automatic dishwasher formulator. An even bigger challenge seems to be presented by the requirement of providing clear items in automatic dishwashing.
Lack of clarity can be manifested as filming and/or spotting on the surface of the washed items. This problem is more of an issue on transparent or translucent items such as glass and plastic items. The causes of filming and/or spotting are not straight forward. Usually it is a combination of the soils on the items, the components of the detergent and the species present in the water used for the dishwashing process. The complex interaction between all these elements is not well understood, but it is clear that the problem of clarity in automatic dishwashing transparent items remains unsolved.
Polyphosphate has been traditionally used to help with cleaning and shine, however environmental considerations have made the automatic dishwashing formulator to move away from the use of polyphosphate, making the shine issue even more challenging. Polyphosphate is also a contributor on the removal of bleachable stains. The removal of these stains is more difficult in the absence of polyphosphate.
Phosphate chemistry is quite complex. Phosphate can be found in a variety of forms, including orthophosphate and polyphosphate. Polyphosphate can come in different forms: pyro-,tripoly-, tetrapoly- and trimeta-phosphate. Film and/or spot formation related to phosphate seems to be specific to the type of phosphate, as well as the cation associated to the phosphate, i.e., it is not the same if the phosphate is in the form of sodium salt, as for example the phosphate coming from the detergent, or in the form of calcium phosphate (coming from the water). This complexity makes shine one of the most challenging and complex issues in automatic dishwashing.
Polyphosphates and/or orthophosphate are used as corrosion inhibitor by some potable water providers. They work by forming a protective film on the interior surface of pipes. It has now been found that the presence of phosphate and more specifically orthophosphate in the wash water negatively impacts detergent performance and in particular the clarity of transparent washed items.
In view of the above discussion there is a need to provide a method of automatic dishwashing that overcomes all or some of the above mentioned problems.